A conventional optical coupling device (for example, a photocoupler) has an internal structure, for example, as shown in FIG. 1. The optical coupling device of FIG. 1 includes a light-emitting element 1, a light-receiving element 2, a light-emitting side lead frame 31, a light-receiving side lead frame 32, a metal wire 4, silicon resin 5, translucent epoxy resin 6, and light-shielding epoxy resin 7.
Further, examples of the lead frame used in the foregoing optical coupling device are shown in FIGS. 2(a), 2(b), 3(a), and 3(b). In the lead frame shown in FIGS. 2(a) and 2(b), header sections 31a for mounting thereon the light-emitting elements 1 and header sections 32a for mounting thereon the light-receiving elements 2 are respectively provided on separate lead frames 31 and 32 in longitudinal directions.
Further, in the lead frame shown in FIGS. 3(a) and 3(b), the header sections 31a are arranged in a matrix between cradle sections 26 of the lead frame 31. Similarly, the header sections 32a are arranged in a matrix between cradle sections 27 of the lead frame 32.
In the following, a manufacturing method of the lead frames 31 and 32 will be explained (briefly). First, the header sections 31a and 32a, which are to be mounted with the elements, are molded on a coiled metal material (a Cu material, a Fe material, etc.) using a punching mold, as shown in FIGS. 2(a) and 2(b), or FIGS. 3(a) and 3(b).
Then, the header sections 31a and 32a and second wire-bonding sections 31b and 32b (see FIGS. 2(a) and 2(b)) are subjected to silver plating, and then the header sections 31a and 32a are bent (see a flowchart of FIG. 4 which shows a manufacturing process of the lead frame. The lead frame is generally manufactured in the process as described above, but the lead frame may be manufactured in a sequential process of the “silver plating”, the “punching”, and the “bending”, or in a sequential process of the “punching”, the “bending”, and the “plating”.
In the optical coupling device, two kinds of the lead frames, which are the lead frame 31 mounted with the light-emitting elements 1 and the lead frame 32 mounted with the light-receiving elements 2, are required as described above, and thus two kinds of punching molds are therefore required. The optical coupling device is manufactured as described below, using the lead frames 31 and 32 shown in FIGS. 2(a) and 2(b), for example.
First, the die-bonding process is carried out for die-bonding (bonding) light-emitting element 1 and the light-receiving element 2 to header sections 31a and 32a of the lead frames 31 and 32 respectively. Then, the wire-bonding is carried out (connecting the light-emitting elements 1 and the light-receiving elements 2 to an external lead using the metal wires 4). Then, the light-emitting elements 1 are coated with the silicon resin 5 for relaxing stress.
Subsequently, the lead frames 31 and 32 are arranged so as to face each other in such a manner that respective optical axes of the light-emitting elements 1 and the light-receiving elements 2 coincide. Then, both lead frames 31 and 32 are bonded to each other by welding. Then, a primary molding is carried out using the translucent epoxy resin 6, and then the transfer molding is carried out on the entire device using the light-shielding epoxy resin 7.
A product is completed after going through respective steps of an exterior plating, a lead forming (external lead processing), an insulation withstand voltage test (insulation test between the primary molding and the secondary molding), an electric property test (measurement of electric properties), a marking, a visual inspection, and a packaging. Note that, other than the transfer molding, an injection molding or a cast molding may be adopted as a molding method. Further, in the primary molding, in replace of the transparent epoxy resin, transparent silicon resin 9 may be adopted to form a path between the light-emitting element 1 and the light-receiving element 2, as shown in FIG. 5.
A manufacturing method of the optical coupling device using the lead frames 31 and 32 shown in FIGS. 3(a) and 3(b) is the same as that using the lead frames 31 and 32 shown in FIGS. 2(a) and 2(b). Conventional examples in accordance with the lead frames 31 and 32 shown in FIGS. 3(a) and 3(b) are disclosed in Japanese Unexamined Patent Publication Nos. 6-237010/1994 (Tokukaihei 6-237010, published on Aug. 23, 1994) and 7-254728/1995 (Tokukaihei 7-254728, published on Oct. 3, 1995), for example. Further, a flowchart showing the manufacturing process and a line block diagram of the conventional optical coupling device are shown in FIGS. 6 and 7.
Incidentally, in recent years, in accordance with intensified price competition in electronic parts, it becomes a critical issue to reduce a fixed cost such as equipment amortization cost as well as variable cost such as material cost. This further makes it critical to increase efficiency in material (to reduce a material cost per electronic part), and to reduce an equipment cost by streamlining an equipment arrangement.
When the conventional lead frame is used, the lead frame for mounting thereon the light-emitting elements and the lead frame for mounting thereon the light-receiving elements are respectively required. Thus, as shown in the flowchart of FIG. 6, which shows a manufacturing method, and the line block diagram of FIG. 7, for example, two separate processing and conveyance systems C1 and C2 are required for respectively performing the die-bonding and the wire-bonding for the respective lead frames.
Namely, it is required to separately arrange (a) the processing and conveyance system C1 on the light-emitting element side, from steps such as the die-bonding, the wire-bonding, and the pre-coating, to a step of superposing and welding the both lead frames with each other, and (b) the processing and conveyance system C2 on the light-receiving element side, from respective steps such as the die-bonding, the wire-bonding, and the pre-coating, to a step of superposing and welding the both lead frames with each other.
Therefore, a large space is required for installing the manufacturing device, and equipment expenses are increased. Further, since two lead frames are required for the light-emitting element side and the light-receiving element side respectively, two molds are required for manufacturing (punching) the lead frames, which, in turn, increases a manufacturing cost, resulting in high costs of the optical coupling device.